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The Great Cretaceous Mass Extinction

The Great Cretaceous Mass Extinction - the correct age In...

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The Great Cretaceous Mass Extinction In 1980, physics Nobel laureate Luis Alvarez (1911 - 1988) with his son, Berkeley geology professorWalter Alvarez (born in 1940), and their coworkers proposed a wild idea: an asteroid had hit the earth 65 million years ago and triggered a series oif events that culminated in the mass extinction that ended the age of dinosaurs. Their discovery of unusually high levels of the rare metal iridium at the boundary layer between the Cretaceous and the Tertiary periods led to a conclusion that the extinction was caused by a 10 km asteroid. Iridium is a rare metal at the Earth's surface, but is known to occur at impact sites, and is also thought to occur deep within the Earth. The major flaw in the hypothesis at that time was the lack of a suitably large impact structure of
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Unformatted text preview: the correct age. In 1991 a team of other scientists found evidence of just such a crater buried off the coast of the villiage of Chicxulub in Yucatan, Mexico. Consequences of the impact were profound. The immense amounts of material ejected from the crater into the atmosphere blocked or reduced sunlight levels, effectively shutting down the process of photosynthesis that is the basis of all food webs. The vaporization of rocks at impact contributed sulfur and nitric acids, which had a severe acid rain effect of vegetation and marine environments. Shocked quartz grains, usually considered diagnostic of an impact site (or a nuclear test site), have been found associated with these deposits....
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